Percussion circuit



. NMQGKD mk NW n ww. m w 5. m II' llll l "l// a if m nyw 1 1 A UE I JNM CH l l FIJ@ |1I-L H E0 jl l: www@ -I I -f w IIHII mw NW Mw Q F SS Feb. 15, 1966 s. cuTLER ETAL PERCUSSION CIRCUIT Original Filed July l, 1957 BY/Uuum TT W ATTORNEY United States Patent O 6 Claims. (Cl. 84-1.26)

This is a continuation of application Serial No. 669,112, filed July 1, 1957, now abandoned.

This invention lrelates to a circuit for applying a modulation envelope, and particularly :a percussive modulation envelope, to a signal, such as a tone signal of an electronic instrument, e.g., an electronic organ.

It is an object of this invention to provide an improved and simplied circuit for giving a percussive effect to an electronic organ.

It is another object of this invention to provide a percussion circuit for electronic organ wherein each note played produces the percussive effect, irrespective of the time intervals between successive notes, and even if successive notes are held down rather than released.

It is a further object of this invention to provide a percussion circuit wherein all notes or keys which are in depressed condition will produce a percussive tone whenever any other note is played or depressed, thus producing a reiterative percussion for an entire depressed chord whenever any note of the keyboard is played.

In accordance with these and other objects which will become apparent hereinafter, a preferred form of the present circuit will now be described with reference to the accompanying drawing:

The single gure of the drawing is a schematic diagram of a circuit embodying the present invention.

Referring to the drawing, the circuit of the present invention comprises a modulation means or modulator indicated by the broken-line ou-tline 11, a pulse or triggering means or keyer indicated by the broken-line outline 12, and a switch assembly or triggering means indicated by the broken-line outline 13. The present invention has particular applicability to a keyboard instrument such as an electric or electronic organ, and there is accordingly illustrated a hand or pedal operated keyboard 14 having a plurality of individually actuable keys corresponding to musical tones or notes. Each key has associated therewith, and actuates, its own individual triggering means 13.

Each triggering means 13 comprises a capacitor 16 connected across the switch arm 17 of a double throw switch and one of the contacts 18 of the switch. The contact 18 is grounded, as shown at 15, and the other contact 19 is connected, by a conductor 20, to the input of a oneshot multivibrator 21, forming ya portion of the keyer 12. The multivibrator 21 consists of a pair of triodes 22 and 23.

The triode 22 is normally not conductive while the triode 23 is normally conductive. Under this condition the full plate voltage from terminal 24 (a source of voltage) resides on the plate of the triode 22. When the switch arm 17 is moved upward, the capacitor 16 is connected to the plate of the triode 22, and the brief charging of the capacitor 16 from the source 24, through the plate resistor 26, causes la short negative spike 27 to appear on the plate 25 of the triode 22. This is transmitted through the coupling capacitor 28 to the grid of the triode 23, causing this tube to block conduction and produce the longer square wave or pulse 29 on the plate of the triode 23.

The pulse 29 is accompanied by a similar pulse on the cathodes of tubes 22 and 23, by virtue of cathode resistor 31, which thus serves to couple the two tubes together. The parameters of the multivibrator 21 are adjusted so that after a given time the circuit relaxes and resumes its normal or quiescent state. Output pulse 29 is applied through capacitor 32, to the grid of a cathode follower 34, as shown at 33.

The output from the cathode follower 34 is applied to the modulator 11, to charge a relatively large capacitor 37, and is returned to the keyer through a bias 38. Bias 38 is a source of positive bias voltage, the negative terminal of which is grounded. Its purposes is to maintain the cathode of tube 34 suiciently positive to cut off current in tube 34 in the absence of a pulse applied to the grid of the tube.

The pulse charge on the capacitor 37 decays through a resistor 39 in parallel with series connected resistors 41 and 42, to form a modulating pulse 43.

The modulating pulse 43 is lapplied to an audio signal 44 placed on the primary winding 46 of an input transformer 47 from an audio amplifier 48. Input to the arnplier 48 comes from a signal or tone generator or generating means 49 through an attenuating resistor 51 that constitutes a percussion attack control. The secondary winding 52 of the input transformer 47 is connected across the primary winding 53 of an output transformer 54, through a pair of non-linear impedance or resistance means 56 and 57, each comprising an instantaneously voltage sensitive, non-polar resistance, known in the trade as a v-aristor. It is not necessary that non-polar resistances be used at this point. For example, any impedance means whose impedance is a function of the voltage across the impedance means, e.g., a non-linear diode, could be used.

The impedance 56 is connected between one output terminal of the transformer 47, Aand one input terminal of the transformer 54 and the impedance 57 is connected between the other output terminal of the transformer 47 and the other input terminal of the transformer 54.

The capacitor 37 is connected. across the respective midpoints 45 and 50 of the windings 52 and 53, so as to be applied as a bias simultaneously across the two impedances 56 and 57. The amplitude of the input signal 44 is sufficiently small that it does not bias the impedance 56 and 57 appreciably into their conducting regions. As a result, when there is no modulating bias from the capacitor 37, only a very small signal passes through the impedances 56 and 57 to the output transformer 54. When the relatively large modulation pulse 43 is applied. across the impedances 56 and 57, their respective resistances or impedances are greatly decreased, allowing a relatively large signal current to ow for the duration of the modulating pulse. The resulting modulated signal 59 appears at the output terminals of the transformer 54, and is applied, to an output amplifier 61, and thence at an output terminal 62 of the entire circuit, through a percussion attack switch 63. Terminal 62 is connected to a suitable utilizing device such as a loudspeaker.

Even without the presence of a modulation pulse 43 on the capacitor 37, the respective impedances of the devices 56 and 57 are not infinite, and some signal 44 leaks through to the output transformer 54. ln order to comlpensate for this leakage, a parallel connected resistor 64 and capacitor 66 are connected diagonally across the bridge circuit composed of the elements 52, 56, 53 and 57. The other diagonal is occupied by a similar compensating impedance in the form of Aresistor 67 and capacitor 68. The combined parallel impedance of 64-66 (and also 67-68) is equal to the impedance of the resistance (which has a certain amount of capacitance) 56, and also, to the impedance 57. The compensating diagonals 64 and 67 serve to balance out and cancel the current that leaks through the resistors S6 and 57 when they are in their high impedance state. When the modulation pulse 43 is applied to the capacitor 37, the impedance of 56 and 57 drops so low that the resistors 64 and 66 become a negligible factor in ther operation of the circuit.

The decay time of the percussive tone 59 is adjusted by the switch 71 and variable resistor 41, being maximum when the switch 71 is open and being minimum when the switch 71 is closed and the potentiometer 41 is adjusted to minimum value. The maximum decay time is determined by the value of the resistor 39 and the minimum delay time by the value of the resistor 42.

Resistor 72 and capacitor 73 are series connected across the secondary winding 52 in order to load the transformer 47 and correct its frequency response. Similar loading is applied to the transformer 54 by resistor 74 and capacitor 76. In the keyer 12, a capacitor 77 is shunted around the grid return resistor 78 in order to take some of the higher frequency components out of the pulse 29 and thereby decrease the key click in the circuit. In order to further prevent radiation of these clicking high frequency components, a low pass filter consisting of resistor 79 and capacitor 81 is inserted in the lead 82 going to the grounding switch portion 83 of the percussion attack switch 63. This filter bypasses the higher frequency components and keeps them from radiating 'from the lead 82.

Each of the keys 14, in addition to inserting its particular percussion capacitor 16 into the present percussion circuit, also serves to actuate its own particular generator switch 84, the closing of `which turns on the particular tone generating means 49 which produces the note or tone corresponding to that particular key 14. This tone, as explained hereinbefore, is applied through the 4adjustable resistor 51, constituting a percussion attack control, to the input of the modulator 11.

The screen grid voltage 86 for the cathode follower 34 is relatively high in order to cause the tube 34 to saturate quickly and thus constitute as closely as possible an on-oif switch.

When percussion is not desired, the switch 63 is in its right posi-tion, wherein the switch arm 83 grounds the lead 82, disabling the cathode follower 34 so that no pulses emanate from the keyer 12. At the same time, the ganged switch a-rm 87 connects the output of the tone generating means -49 directly to the output terminal 62, by-passing the modulating circuit 11 completely.

When percussion is desired, the percussion attack switch v63 is placed in its left position, ungrounding the lead 82,

and permitting the keyer 12 to pulse the modulator 11; at the same time the output from the tone generating means 49 is diverted through the modulator 11 and thence to the output terminal 62.

An eminently satisfactory percussion circuit having the following parameters has been constructed and operated satisfactorily Capacitor 32-.1 mfd.

Capacitor 77-.01 mfd.

Resistor 78-1 megohm Resistor 7 9--100 kilohms Capacitor `81--.033 mfd.

Resistor 97--5 6 kilohms Resistor 98-56 kilohms Resistor 99--100 kilohms Capacitor 101-2 mfd.

Resistor 102-100 kilohms Tubes 48 and'61-l2AU7 (double triode) Capacitor 10S-.01 mfd.

Resistor 104-1 megohm Resistor 105--1 kilohm Capacitor y107-27 mfd.

Capacitor 73-.1 mfd.

Resistor 72-27 kilohms Resistors 64 and V67--2.7 megohms Capacitors 66 and `625-120 mmfd. Resistor 39-100 kilohms Capacitor 37-4 mfd.

Resistor 42-15 kilohms Adjustable resistor 41--1 megohm `Capacitor 76-.022 mfd.

Resistor 74-4.7 kilohms Resistor 10S-2.7 kilohms Capacitor 109-.01 mfd.

Resistor 110-fl megohm Adjustable resistor 51-1 megohm, maximum Resistor 111-47 kilohms Complete operation of the circuit of the present invention will now be briefly reviewed. When a given key or note 14 is struck, its corresponding switches 17 and 84 are closed. The latter actuates a corresponding appropriate tone generating means 49 to apply -a given audio tone to the input of the amplifier 48 of the modulator 11. Simultaneously, the charging of the capacitor 16 produces a negative spike 27 on the one shot multivibrator 21, which'is formed into the pulse 43 by the cathode follower 34. This pulse is applied across the capacitor 37, which discharges mainly through the resistor 39.

The pulse 43 constitutes a bias across the two non- 'linear resistors 56 and 57, markedly lowering their resistance, and greatly increasing the transmissability from the input transformer 47 to the output transformer 54. This permits the signal 44 applied to the input transformer 47 to be placed in modulated form on the transformer 54, and it appears at the output terminals of the transformer `as the pulse-modulated signal 59. This is the percussive note which is applied through the amplifier 61 to the output terminal 62.

If now, while the rst key 14 remains depressed, a second key 14 is operated, a succeeding percussive tone 59 will be made to appear at the output terminal 62, and this second tone will contain both the first and second pitch since the two-tone generating'means are both now connected to the circuit by depression or closing of their two respective switches 84. The same applies for yan entire cho-rd, so that if a chord of notes or keys is held depressed, there will be repetitive percussive sounding of the entire chord whenever any additional note is depressed, to refpulse the keyer 12 by switching in another capacitor 16. Thus, the oneshot multi-vibrator 21 can be successively re-triggered by spikes 27 at any given interval not shorter than the duration of pulse 29, which as stated is approximately 1&0 of a second.

yWhile fthe instant invention has been shown and described herein in what is conceived to be the most prac` tical and preferred embodiment, it is recognized that de` partures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein, `but is to be accorded the. full scope of the claims.

What is claimed is:

1. In a percussion circuit for a musical instrument having a keyboard with a plurality of digitally operable keys and a plurality of audio tone generators of differing pitch corresponding to said keys:

a plurality of individual capacitors corresponding respectively to said keys,

a plurality of switches corresponding respectively to said capacitors and said keys,

means for causing said switches to be actuated lby the respective keys,

first circuit means for connecting said capacitors to the respective switches,

modulating means connected to said generators and effective to pass audio tone during the presence of a pulse applied thereto, and

second circuit means responsive to the state of charge on said capacitors for applying a pulse to said modulating means upon actuation of any of said switches, irrespective of the operative condition of any other switch, thereby to cause a percussive audio tone to pass through said modulating means.

2. In a percussion circuit for a musical instrument having a keyboard with a plurality yof digitally operable keys and a plurality of audio tone generators of differing pitch corresponding to said keys:

a plurality of individual capacitors corresponding respectively to said keys,

a plurality of switches corresponding respectively to said capacitors and said keys,

means for causing said switches to be actuated by the respective keys,

first circuit means for connecting said capacitors to the respective switches, modulating means connected to said generators and effective to pass audio tone during the presence of a pulse applied thereto, and

second circuit means for connecting each of said switches to said modulating means irrespective of the operative condition of any other switch, and responsive to the state of charge on a respective capacitor, to apply a pulse to said modulating means upon each actuation of a switch, and thus cause a percussive audio tone to pass through said modulating means.

3. In a percussion circuit for musical instrument having a keyboard with a plurality of digitally operable keys and a plurality of audio tone generators of differing pitch corresponding to said keys:

pulse means for delivering an output pulse in response to each input pulse applied thereto,

a plurality of switches corresponding to said keys,

a corresponding plurality of capacitive means for effecting an input pulse upon switch actuation,

rst circuit means for electrically connecting said capacitors to the respective switches,

second circuit means for connecting each of said switches to said pulse means for delivering to said pulse means an input pulse upon operation of any of said switches,

and means for effecting percussive delivery of audio tones in response to each pulse delivered by said pulse means.

4. In a percussion circuit for musical instnnment having a keyboard with a plurality of digitally operable keys and a plurality of audio tone generators of differing pitch corresponding to said keys:

pulse means for delivering an output pulse in response to each input pulse applied thereto,

a plurality of capacitors corresponding to said keys,

a corresponding plurality of switches connected electrically to said capacitors, each of said switches being connected to said pulse means for actuating said pulse means from said capacitors upon operation of any of said switches to alter its circuit relation to said pulse means,

modulating means connected to said generators and effective to pass audio tone during the presence of a pulse applied thereto,

and means for applying a pulse from said pulse means to said modulating means.

5. In a percussion circuit for a musical instrument having a keyboard with a plurality of digitally operable keys, and a plurality of audio tone generators of differing pitch corresponding to said keys:

pulse means for delivering an output pulse in response to each input pulse applied thereto,

a plurality of individual capacitors corresponding respectively to said keys,

a plurality of switches corresponding respectively to said capacitors and said keys,

means for causing said switches to be actuated by the respective keys,

first circuit means for connecting said capacitors to the respective switches,

modulating means connected to said generators, and effective to pass audio tone during the presence of a pulse applied thereto,

second circuit means for applying a pulse from said capacitors to said pulse means upon actuation of any of said switches irrespective of the operative condition of any other switch,

and third circuit means for applying a pulse from the output of said pulse means to said modulating means, thereby to cause a percussive audio tone to pass through said modulating means upon each actuation of a switch.

6. In a percussion circuit for musical instrument having a keyboard with a plurality of digitally operable keys and a plurality of audio tone generators of differing pitch corresponding to said keys:

pulse means for generating a single pulse in response to each triggering stimulus applied thereto,

a plurality of triggering capacitors corresponding to said keys,

a corresponding plurality of switches connected electrically to said capacitors, each of said switches being connected to said pulse means for actuating said pulse means from said capacitors upon operation of any of said switches to alter its circuit relation t0 said pulse means.

modulating means connected to said generators and effective to pass audio tone during the presence of a pulse applied thereto,

and means for applying a pulse from said pulse means to said modulating means.

References Cited by the Examiner UNITED STATES PATENTS 2,169,842 9/1939 Kannenburg SLi-1.26 X 2,486,208 10/ 1949 Rienstra Slt-1.26 2,783,672 3/1957 Hanert 84-l.26

GEORGE N. WESTBY, Primary Examiner. 

1. IN A PERCUSSION CIRCUIT FOR A MUSICAL INSTRUMENT HAVING A KEYBOARD WITH A PLURALITY OF DIGITALLY OPERABLE KEYS AND A PLURALITY OF AUDIO TONE GENERATORS OF DIFFERING PITCH CORRESPONDING TO SAID KEYS: A PLURALITY OF INDIVIDUAL CAPACITORS CORRESPONDING RESPECTIVELY TO SAID KEYS, A PLURALITY OF SWITCHES CORRESPONDING RESPECTIVELY TO SAID CAPACITORS AND SAID KEYS, MEANS FOR CAUSING SAID SWITCHES TO BE ACTUATED BY THE RESPECTIVE KEYS, FIRST CIRCUIT MEANS FOR CONNECTING SAID CAPACITORS TO THE RESPECTIVE SWITCHES, MODULATING MEANS CONNECTING SAID CAPACITORS TO THE EFFECTIVE TO PASS AUDIO TONE DURING THE PRESENCE OF A PULSE APPLIED THERETO, AND SECOND CIRCUIT MEANS RESPONSIVE TO THE STATE OF CHARGE ON SADI CAPACITORS FOR APPLYING A PULSE TO SAID MODULATING MEANS UPON ACTUATION TO ANY OF SAID SWITCHES, IRRESPECTIVE OF THE OPERATIVE CONDITION OF ANY OTHER SWITCH, THEREBY TO CAUSE A PERCUSSIVE AUDIO TONE TO PASS THROUGH SAID MODULATING MEANS. 